Perfusion

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Perfusion
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• Histology means the science of the tissues.
• Tissue an aggregation of cells that have become
  specialized in a manner characteristic of their
  development.
• A specimen usually a very small part of an
  organism.
• Histological technique is the science of
  preparing organs, tissues, or tissue components
  for observation and study.
• Advancements in our knowledge of the
  microscopical anatomy of both animals and plants
  have come from the study of histological
  specimens.
• First step ? Perfusion

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• Perfusion Forcing the fixing fluid through
  blood vessels by introducing it into an artery
  and allowing it to escape through an opened vein

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• Living able to perform variety of metabolic
  activities.
• There are progressive changes that occur in
  tissues after death, and these are very likely to
  affect the subsequent staining and appearance of
  the finished histological section. As a general
  rule it is desirable to fix tissue from the
  living state and thereby avoid postmortem
  deterioration.
• Fixing, or fixation, refers specifically to the
  coagulation of tissue proteins and applies to
  fresh, though dead, tissues, as well as living
  ones.

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• Fixatives have a hardening effect on soft tissues
  and prevent deterioration and other misleading
  structural changes in cells and tissues.

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Fixatives

• Coagulate proteins.
• Prevent cellular enzymes from digesting the cells
  from which they are released at death (postmortem
  degeneration), which would spoil tissue for
  microscopic study.
• By coagulating proteins fixatives also imprison
  carbohydrate and fat containing
  macromolecules, which would otherwise escape as a
  result of tissue processing.
• Are usually strongly antiseptic, killing bacteria
  and other disease containing agents in infected
  tissues that would otherwise pose a hazard to the
  health of those handling such tissue.

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• Formaldehyde penetrate tissue easily
• Formalin fixes by causing a change in the
  chemical structure of protein molecules (binds
  tie the amino acids).
• We will use a 4 aqueous solution of formaldehyde
  buffered to neutral pH (i.e. 7.4).

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• If the fixing fluid to be used for perfusion
  cause coagulation of the blood, the blood should
  be first washed out by a preliminary perfusion
  with physiological salt solution.
• A buffer solution is defined as one that will
  tolerate the addition of H ion or OH ion in
  considerable quantity without effecting a marked
  change in its pH value. The key to this type of
  chemical behavior is to be found in the reserve
  or potential supply of ions possessed by weak
  acids or bases.
• Phosphate buffer a salt or ester of phosphoric
  acid which is a weak acid.

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